Method of fabricating a thin-film device

ABSTRACT

A method of forming a thin-film device includes forming an oxide-semiconductor film formed on the first electrical insulator, and forming a second electrical insulator formed on the oxide-semiconductor film, the oxide-semiconductor film defining an active layer. The oxide-semiconductor film is comprised of a first interface layer located at an interface with the first electrical insulating insulator, a second interface layer located at an interface with the second electrical insulator, and a bulk layer other than the first and second interface layers. The method further includes oxidizing the oxide-semiconductor film to render a density of oxygen holes in at least one of the first and second interlayer layers is smaller than a density of oxygen holes in the bulk layer.

CROSS REFERENCE TO RELATED APPLICATION

The present application is a divisional application of U.S. patentapplication Ser. No. 11/890,426 filed on Aug. 6, 2007 the entirecontents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a thin-film device, and a method of fabricatingthe same.

2. Description of the Related Art

A transparent electrically conductive film composed of oxide, such as anITO film composed of compound of indium (In), tin (Sn), and oxygen (O),is frequently used in a flat panel display or a photoelectric transferdevice, since it has a sheet resistance of a few ohms per a unit areaeven if it has a small thickness such as hundreds of nanometers, and ithas high transmittance to visible light.

Furthermore, a study to a thin-film transistor including a channel layercomposed of transparent oxide semiconductor such as In—Ga—Zn—O has beenrecently started. Such oxide semiconductor contains highly ionic bonds,and is characterized by a small difference in electron mobility betweencrystalline state and amorphous state. Accordingly, relatively highelectron mobility can be obtained even in amorphous state.

Since an amorphous film of oxide semiconductor can be formed at roomtemperature by carrying out sputtering, a study about a thin-filmtransistor composed of oxide semiconductor to be formed on a resinsubstrate such as a PET substrate has been started.

For instance, a thin-film transistor composed of oxide semiconductor issuggested in Japanese Patent Application Publication No. 2005-033172(paragraph 0041), Japanese Patent Application Publication No.2003-179233 (paragraphs 0014-0016), Japanese Patent ApplicationPublication No. 2003-86808 (paragraph 0053), Japanese Patent ApplicationPublication No. 2003-60170 (paragraph 0037), and Japanese PatentApplication Publication No. 2006-502597 (paragraphs 0021-0023).

In a thin-film transistor composed of oxide semiconductor, donor defectscaused by oxygen holes existing in a semiconductor film, in particular,oxygen holes existing at an interface layer between a semiconductor filmand an electrically insulating film exert much influence on electriccharacteristics of the thin-film transistor.

The above listed Publications are accompanied with a problem ofinsufficient control to oxygen holes existing at an interface layer.

In particular, Japanese Patent Application Publication No. 2006-502597alleges that it is possible to reduce oxygen holes by annealing oxidesemiconductor at 300 degrees centigrade or higher in oxidationatmosphere. Though such annealing may be effective to reduction inoxygen holes existing at an upper surface of an oxide-semiconductorfilm, such annealing is not effect to reduction in oxygen holes existingat a lower surface of an oxide-semiconductor film (that is, a region ofoxide semiconductor close to an interface between an underlyinginsulating film and oxide semiconductor formed on the underlyinginsulating film). This is because such annealing is difficult topenetrate an oxide-semiconductor film.

It may be possible to oxidize even a lower surface of anoxide-semiconductor film by carrying out annealing at 600 degreescentigrade or higher for enhancing penetration of oxidation, however, inwhich case, there would be caused problems that it is not possible touse a cheap glass substrate as an electrically insulating substrate, andthat if a metal film exists below an oxide-semiconductor film, annealingcauses metal of which the metal film is composed to diffuse into theoxide-semiconductor film, and resultingly, the oxide-semiconductor filmis contaminated.

Thus, it was not possible to fabricate a thin-film transistor composedof oxide semiconductor and having desired characteristics sufficientlyapplicable to a display driver, on a cheap glass substrate with highreproducibility and high fabrication yield.

SUMMARY OF THE INVENTION

In view of the above-mentioned problems in the related art, it is anexemplary object of the present invention to provide a thin-film devicesuch as a thin-film transistor, which is capable of controllinggeneration of oxygen holes at an interface layer, and providing desiredcharacteristics.

It is further an exemplary object of the present invention to provide amethod of fabricating the above-mentioned thin-film device with highreproducibility and high fabrication yield.

In a first exemplary aspect of the present invention, there is provideda thin-film device including a first electrical insulator, anoxide-semiconductor film formed on the first electrical insulator, and asecond electrical insulator formed on the oxide-semiconductor film, theoxide-semiconductor film defining an active layer, theoxide-semiconductor film being comprised of a first interface layerlocated at an interface with the first electrical insulating insulator,a second interface layer located at an interface with the secondelectrical insulator, and a bulk layer other than the first and secondinterface layers, a density of oxygen holes in at least one of the firstand second interlayer layers being smaller than a density of oxygenholes in the bulk layer.

In a second exemplary aspect of the present invention, there is provideda method of fabricating a thin-film device, including forming anoxide-semiconductor film on a first electrical insulator, forming asecond electrical insulator on the oxide-semiconductor film, theoxide-semiconductor film defining an active layer, theoxide-semiconductor film being comprised of a first interface layerlocated at an interface with the first electrical insulating insulator,a second interface layer located at an interface with the secondelectrical insulator, and a bulk layer other than the first and secondinterface layers, and oxidizing the oxide-semiconductor film to render adensity of oxygen holes in at least one of the first and secondinterlayer layers smaller than a density of oxygen holes in the bulklayer.

There is further provided a method of fabricating a thin-film device,including forming an oxide-semiconductor film on a first electricalinsulator, and forming a second electrical insulator on theoxide-semiconductor film, the oxide-semiconductor film defining anactive layer, the oxide-semiconductor film being formed by repeatedlycarrying out formation of an oxide-semiconductor film and oxidation tothe oxide-semiconductor film, the oxide-semiconductor film beingcomprised of a first interface layer located at an interface with thefirst electrical insulating insulator, a second interface layer locatedat an interface with the second electrical insulator, and a bulk layerother than the first and second interface layers, a density of oxygenholes in at least one of the first and second interlayer layers beingsmaller than a density of oxygen holes in the bulk layer.

There is still further provided a method of fabricating a thin-filmdevice, including forming an oxide-semiconductor film on a firstelectrical insulator, forming a second electrical insulator on theoxide-semiconductor film, the oxide-semiconductor film defining anactive layer, the oxide-semiconductor film being formed by repeatedlycarrying out formation of an oxide-semiconductor film and oxidation tothe oxide-semiconductor film, and oxidizing the oxide-semiconductor filmto render a density of oxygen holes in at least one of the first andsecond interlayer layers smaller than a density of oxygen holes in thebulk layer.

The above and other objects and advantageous features of the presentinvention will be made apparent from the following description made withreference to the accompanying drawings, in which like referencecharacters designate the same or similar parts throughout the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view, each showing a step to be carried outin a method of fabricating a thin-film device in accordance with thefirst exemplary embodiment.

FIG. 2 is a cross-sectional view, each showing a step to be carried outin a method of fabricating a thin-film device in accordance with thefirst exemplary embodiment.

FIG. 3 is a cross-sectional view, each showing a step to be carried outin a method of fabricating a thin-film device in accordance with thefirst exemplary embodiment.

FIG. 4 is a cross-sectional view, each showing a step to be carried outin a method of fabricating a thin-film device in accordance with thefirst exemplary embodiment.

FIG. 5 is a cross-sectional view, each showing a step to be carried outin a method of fabricating a thin-film device in accordance with thefirst exemplary embodiment.

FIG. 6 is a cross-sectional view, each showing a step to be carried outin a method of fabricating a thin-film device in accordance with thefirst exemplary embodiment.

FIG. 7 is a cross-sectional view, each showing a step to be carried outin a method of fabricating a thin-film device in accordance with thefirst exemplary embodiment.

FIG. 8 is a cross-sectional view, each showing a step to be carried outin a method of fabricating a thin-film device in accordance with thefirst exemplary embodiment.

FIG. 9 is a cross-sectional view, each showing a step to be carried outin a method of fabricating a thin-film device in accordance with thesecond exemplary embodiment.

FIG. 10 is a cross-sectional view, each showing a step to be carried outin a method of fabricating a thin-film device in accordance with thesecond exemplary embodiment.

FIG. 11 is a cross-sectional view, each showing a step to be carried outin a method of fabricating a thin-film device in accordance with thesecond exemplary embodiment.

FIG. 12 is a cross-sectional view, each showing a step to be carried outin a method of fabricating a thin-film device in accordance with thesecond exemplary embodiment.

FIG. 13 is a cross-sectional view, each showing a step to be carried outin a method of fabricating a thin-film device in accordance with thesecond exemplary embodiment.

FIG. 14 is a cross-sectional view, each showing a step to be carried outin a method of fabricating a thin-film device in accordance with thesecond exemplary embodiment.

FIG. 15 is a cross-sectional view, each showing a step to be carried outin a method of fabricating a thin-film device in accordance with thethird exemplary embodiment.

FIG. 16 is a cross-sectional view, each showing a step to be carried outin a method of fabricating a thin-film device in accordance with thethird exemplary embodiment.

FIG. 17 is a cross-sectional view, each showing a step to be carried outin a method of fabricating a thin-film device in accordance with thethird exemplary embodiment.

FIG. 18 is a cross-sectional view, each showing a step to be carried outin a method of fabricating a thin-film device in accordance with thethird exemplary embodiment.

FIG. 19 is a cross-sectional view, each showing a step to be carried outin a method of fabricating a thin-film device in accordance with thethird exemplary embodiment.

FIG. 20 is a cross-sectional view, each showing a step to be carried outin a method of fabricating a thin-film device in accordance with thefourth exemplary embodiment.

FIG. 21 is a cross-sectional view, each showing a step to be carried outin a method of fabricating a thin-film device in accordance with thefourth exemplary embodiment.

FIG. 22 is a cross-sectional view, each showing a step to be carried outin a method of fabricating a thin-film device in accordance with thefourth exemplary embodiment.

FIG. 23 is a cross-sectional view, each showing a step to be carried outin a method of fabricating a thin-film device in accordance with thefourth exemplary embodiment.

FIG. 24 is a cross-sectional view, each showing a step to be carried outin a method of fabricating a thin-film device in accordance with thefourth exemplary embodiment.

FIG. 25 is a cross-sectional view, each showing a step to be carried outin a method of fabricating an oxide-semiconductor film in accordancewith the fourth exemplary embodiment.

FIG. 26 is a cross-sectional view, each showing a step to be carried outin a method of fabricating an oxide-semiconductor film in accordancewith the fourth exemplary embodiment.

FIG. 27 is a cross-sectional view, each showing a step to be carried outin a method of fabricating an oxide-semiconductor film in accordancewith the fourth exemplary embodiment.

FIG. 28 is a cross-sectional view, each showing a step to be carried outin a method of fabricating an oxide-semiconductor film in accordancewith the fourth exemplary embodiment.

FIG. 29 is a cross-sectional view, each showing a step to be carried outin a method of fabricating an oxide-semiconductor film in accordancewith the fourth exemplary embodiment.

DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

Exemplary embodiments in accordance with the present invention will beexplained hereinbelow with reference to drawings.

First Exemplary Embodiment

FIGS. 1 to 8 are cross-sectional views of a thin-film device 100, eachshowing a step to be carried out in a method of fabricating a thin-filmdevice 100 in accordance with the first exemplary embodiment.

A thin-film device 100 in the first exemplary embodiment is comprised ofa bottom gate stagger type thin-film transistor.

Hereinbelow is explained a method of fabricating the thin-film device100.

First, as illustrated in FIG. 1, a gate metal film is formed on anelectrically insulating substrate 10, and then, the gate metal film ispatterned into a gate electrode 11.

Then, a gate insulating film 12 as a first electrical insulator isformed on the electrically insulating substrate 10 so as to cover thegate electrode 11 therewith.

Then, as illustrated in FIG. 2, first oxidation 131 is applied to thegate insulating film 12 without exposing a device (that is, theelectrically insulating substrate 10, the gate electrode 11, and thegate insulating film 12) to atmosphere.

The first oxidation 131 is comprised of application of oxygen plasma,for instance.

The first oxidation 131 causes oxygen to be adhered to a surface of thegate insulating film 12. This ensures that if oxygen deficiency weregenerated at a surface of the gate insulating film, 12, it would bepossible to remove the oxygen deficiency.

Following the first oxidation 131, as illustrated in FIG. 3, anoxide-semiconductor film 14 is formed on the gate insulating film 12without exposing to atmosphere.

As a result, a first interface layer 14A which is a portion of theoxide-semiconductor film 14 located at an interface with the gateinsulating film 12 is oxidized by oxygen having been adhered to asurface of the gate insulating film 12.

Thus, oxygen hole defect can be reduced in the first interface layer 14Aas a part of the oxide-semiconductor film 14.

Specifically, a density of oxygen holes in the first interface layer 14Aof the oxide-semiconductor film 14 becomes smaller than a density ofoxygen holes in a bulk layer 14B of the oxide-semiconductor film 14.

Then, as illustrated in FIG. 4, the oxide-semiconductor film 14 ispatterned.

Then, as illustrated in FIG. 5, reduction 15 is applied to theoxide-semiconductor film 14. For instance, the reduction 15 is comprisedof application of reducing plasma.

As a result, oxygen hole defect is generated at a surface 14C of theoxide-semiconductor film 14.

Specifically, a density of oxygen holes in the surface 14C of theoxide-semiconductor film 14 becomes higher than a density of oxygenholes in the bulk layer 14B of the oxide-semiconductor film 14.

As illustrated in FIG. 6, a source/drain metal film is formed so as toentirely cover the gate insulating film 12 and the oxide-semiconductorfilm 14 therewith, and then, the source/drain metal film is patternedinto source/drain electrodes 16 one of which is a source electrode andthe other is a drain electrode.

It is preferable that the reduction 15 (see FIG. 5) and the subsequentformation of the source/drain metal film are carried out successivelywithout exposing to atmosphere.

Then, as illustrated in FIG. 7, second oxidation 132 is applied to theoxide-semiconductor film 14 through an opening 16A formed between thesource and drain electrodes 16. For instance, the second oxidation 132is comprised of application of oxygen plasma.

As a result, a second interface layer 14E, that is, a portion of thesurface 14C (see FIG. 6) of the oxide-semiconductor film 14, exposedoutside through the opening 16A, is oxidized with the result ofreduction in oxygen hole defects existing at the second interface layer14E.

Thus, a density of oxygen holes in the second interface layer 14E of theoxide-semiconductor film 14 becomes smaller than a density of oxygenholes in the bulk layer 14B of the oxide-semiconductor film 14.

A portion of the surface 14C (see FIG. 6) of the oxide-semiconductorfilm 14 other than the second interface layer 14E, that is, a portion ofthe oxide-semiconductor film 14 existing at an interface with the sourceand drain electrodes 16 defines a third interface layer 14D.

Then, as illustrated in FIG. 8, there is formed a protection insulatingfilm 18 as a second electrical insulator so as to cover the source anddrain electrodes 16 therewith and further cover the oxide-semiconductorfilm 14 therewith at the opening 16A formed between the source electrode16 and the drain electrode 16.

Thus, there is fabricated the thin-film device 100.

It is preferable that the second oxidation 132 (see FIG. 7) and thesubsequent formation of the protection insulating film 18 are carriedout successively without exposing to atmosphere.

The first interface layer 14A which is a portion of theoxide-semiconductor film 14 located at an interface with the gateinsulating film 12 has a density of oxygen holes in the range of 1×10¹²cm⁻³ to 1×10¹⁸ cm⁻³ both inclusive, for instance.

The bulk layer 14B which is a portion of the oxide-semiconductor film 14has a density of oxygen holes in the range of 1×10¹⁶ cm⁻³ to 1×10²⁰ cm⁻³both inclusive, for instance.

A density of oxygen holes of each of the first interface layer 14A andthe bulk layer 14B can be controlled by controlling conditions underwhich they are formed. Specifically, if a density of oxygen inatmosphere is increased during they are being formed, it would bepossible to reduce a density of oxygen holes of them, and if a densityof oxygen in atmosphere is reduced during they are being formed, itwould be possible to increase a density of oxygen holes of them.

The oxidation 131 illustrated in FIG. 2 makes it possible to optimallyreduce an electron density in the first interface layer 14A, ensuringthat the thin-film device 100 can has superior switching characteristic,specifically, five or more columns (1×10⁴ or greater) in an ON/OFF ratioof a drain current.

The third interface layer 14D which is a portion of theoxide-semiconductor film 14 located at an interface with the source anddrain electrodes 16 has a density of oxygen holes in the range of 1×10¹⁹cm⁻³ to 1×10²² cm⁻³ both inclusive, for instance.

The second interface layer 14E which is a portion of theoxide-semiconductor film 14 located at an interface with the protectioninsulating film 18 has a density of oxygen holes in the range of 1×10¹⁶cm⁻³ to 1×10²⁰ cm⁻³ both inclusive, for instance.

A density of oxygen holes of each of the third interface layer 14D andthe second interface layer 14E can be controlled by controllingconditions under which they are formed. Specifically, if a density ofoxygen in atmosphere is increased during they are being formed, it wouldbe possible to reduce a density of oxygen holes of them, and if adensity of oxygen in atmosphere is reduced during they are being formed,it would be possible to increase a density of oxygen holes of them.

The reduction 15 illustrated in FIG. 5 makes it possible to optimallyincrease an electron density in the third interface layer 14D, ensuringthat the third interface layer 14D can have functions as an ohmiccontact layer.

The oxidation 132 illustrated in FIG. 7 makes it possible to optimallyreduce an electron density in the second interface layer 14E, ensuringthat an off current caused by a back-channel electron current can beeffectively reduced.

In the thin-film device 100 including a multi-layered structurecomprised of, in this order, the gate electrode 11, the gate insulatingfilm (first electrical insulator) 12, the oxide-semiconductor film 14,the source and drain electrodes 16, and the protection insulating film(second electrical insulator) 18, it is possible to control the defect(that is, generation of excessive electron donors) caused by oxygenholes existing at an interface between the oxide-semiconductor film 14and the insulating films 12, 18.

That is, it is possible to positively generate oxygen holes in a regionin which oxygen holes are required, and prevent generation of oxygenholes in a region in which oxygen holes are not required.

Specifically, it is possible to reduce the defect caused by oxygen holesin the first interface layer 14A located at an interface with the gateinsulating film 12, by carrying out the first oxidation 131 illustratedin FIG. 2, and then, forming the oxide-semiconductor film 14 asillustrated in FIG. 3. That is, a density of oxygen holes in the firstinterface layer 14A can be made smaller than a density of oxygen holesin the bulk layer 14B.

The reduction 15 illustrated in FIG. 5 positively facilitates togenerate oxygen hole defect in the surface 14C of theoxide-semiconductor film 14 (specifically, the third interface layer 14D(see FIGS. 7 and 8) which is a portion of the surface 14C located at aninterface with the source and drain electrodes 16), and causes the thusgenerated oxygen hole defect to act as electron donors to thereby makethe third interface layer 14D located at an interface with the sourceand drain electrodes 16, become an N-type layer, ensuring increasedpossibility of formation of ohmic contact junction.

The second oxidation 132 illustrated in FIG. 7 makes it possible toreduce oxygen hole defect in the second interface layer 14E which is aportion of the surface 14C of the oxide-semiconductor film 14 exposedthrough the opening 16A, ensuring that an off current in the thin-filmdevice 100 can be reduced.

Second Exemplary Embodiment

FIGS. 9 to 14 are cross-sectional views of a thin-film device 200, eachshowing a step to be carried out in a method of fabricating a thin-filmdevice 200 in accordance with the second exemplary embodiment.

A thin-film device 200 in the second exemplary embodiment is comprisedof a top gate stagger type thin-film transistor.

Hereinbelow is explained a method of fabricating the thin-film device200.

As illustrated in FIG. 9, an underlying insulating film (firstelectrical insulator) 21 is formed on an electrically insulatingsubstrate 10. Then, a source/drain metal film is formed on theunderlying insulating film 21, and subsequently, the source/drain metalfilm is patterned into source and drain electrodes 16 (one of which is asource electrode, and the other is a drain electrode).

Then, as illustrated in FIG. 10, first oxidation 131 is applied to theunderlying insulating film 21.

The first oxidation 131 is comprised of application of oxygen plasma,for instance.

The first oxidation 131 causes oxygen to be adhered to a surface of theunderlying insulating film 21. This ensures that if oxygen deficiencywere generated at a surface of the underlying insulating film 21, itwould be possible to remove the oxygen deficiency.

Following the first oxidation 131, an oxide-semiconductor film 14 isformed on the underlying insulating film 21 and the source/drainelectrodes 16. Then, the oxide-semiconductor film 14 is patterned into adesired shape, as illustrated in FIG. 11.

As a result, a first interface layer 14A which is a portion of theoxide-semiconductor film 14 located at an interface with the underlyinginsulating film 21 is oxidized by oxygen having been adhered to asurface of the underlying insulating film 21.

Thus, oxygen hole defect can be reduced in the first interface layer 14Aas a part of the oxide-semiconductor film 14.

Specifically, a density of oxygen holes in the first interface layer 14Aof the oxide-semiconductor film 14 becomes smaller than a density ofoxygen holes in a bulk layer 14B of the oxide-semiconductor film 14.

It is preferable that the first oxidation 131 illustrated in FIG. 10 andthe formation of the oxide-semiconductor film 14 are successivelycarried out without exposing to atmosphere.

Then, as illustrated in FIG. 12, second oxidation 132 is applied to theoxide-semiconductor film 14. For instance, the second oxidation 132 iscomprised of application of oxygen plasma.

As a result, a second interface layer 14E, that is, a surface 14C of theoxide-semiconductor film 14, is oxidized with the result of reduction inoxygen hole defects existing at the second interface layer 14E.

Thus, a density of oxygen holes in the second interface layer 14E of theoxide-semiconductor film 14 becomes smaller than a density of oxygenholes in the bulk layer 14B of the oxide-semiconductor film 14.

Then, as illustrated in FIG. 13, there is formed a gate insulating film12 as a second electrical insulator so as to cover theoxide-semiconductor film 14 and the source and drain electrodes 16therewith out exposing to atmosphere.

Then, as illustrated in FIG. 14, a gate electrode 11 is formed on thegate insulating film 12.

Then, a protection insulating film 18 is formed on the gate insulatingfilm 12 so as to cover the gate electrode 11 therewith.

Thus, there is fabricated the thin-film device 200.

In the thin-film device 200 including a multi-layered structurecomprised of, in this order, the underlying insulating film (firstelectrical insulator) 21, the source and drain electrodes 16, theoxide-semiconductor film 14, the gate insulating film (second electricalinsulator) 12, the gate electrode 11, and the protection insulating film18, it is possible to control the defect caused by oxygen holes existingat an interface between the oxide-semiconductor film 14 and theinsulating films 21, 12.

Specifically, it is possible to reduce the defect caused by oxygen holesin the first interface layer 14A located at an interface with theunderlying insulating film 21, by carrying out the first oxidation 131illustrated in FIG. 10, and then, forming the oxide-semiconductor film14 as illustrated in FIG. 11. That is, a density of oxygen holes in thefirst interface layer 14A can be made smaller than a density of oxygenholes in the bulk layer 14B.

The second oxidation 132 illustrated in FIG. 12 makes it possible toreduce oxygen hole defect in the second interface layer 14E located atan interface with the gate insulating film 12 to thereby optimallyreduce an electron density in the second interface layer 14E, ensuringthat an off current of the thin-film device 200 caused by a back-channelelectron current can be effectively reduced.

Third Exemplary Embodiment

FIGS. 15 to 19 are cross-sectional views of a thin-film device 300, eachshowing a step to be carried out in a method of fabricating a thin-filmdevice 300 in accordance with the third exemplary embodiment.

A thin-film device 300 in the third exemplary embodiment is comprised ofa top gate planar type thin-film transistor.

Hereinbelow is explained a method of fabricating the thin-film device300.

First, as illustrated in FIG. 15, an underlying insulating film 21 as afirst electrical insulator is formed on an electrically insulatingsubstrate 10.

Then, first oxidation 131 is applied to the underlying insulating film21.

The first oxidation 131 is comprised of application of oxygen plasma,for instance.

Then, as illustrated in FIG. 16, an oxide-semiconductor film 14 isformed on the underlying insulating film 21 without exposing toatmosphere.

The first oxidation 131 causes oxygen to be adhered to a surface of theunderlying insulating film 21. A first interface layer 14A which is aportion of the oxide-semiconductor film 14 located at an interface withthe underlying insulating film 21 is oxidized by oxygen having beenadhered to a surface of the underlying insulating film 21.

Thus, oxygen hole defect can be reduced in the first interface layer 14Aas a part of the oxide-semiconductor film 14.

Specifically, a density of oxygen holes in the first interface layer 14Abecomes smaller than a density of oxygen holes in a bulk layer 14B ofthe oxide-semiconductor film 14.

Then, as illustrated in FIG. 16, the oxide-semiconductor film 14 ispatterned.

Then, as illustrated in FIG. 16, second oxidation 132 is applied to theoxide-semiconductor film 14. For instance, the second oxidation 132 iscomprised of application of oxygen plasma.

As a result, since a second interface layer 14E located at a surface ofthe oxide-semiconductor film 14, oxygen hole defect is reduced in thesecond interface layer 14E.

Specifically, a density of oxygen holes in the second interface layer14E becomes smaller than a density of oxygen holes in the bulk layer 14Bof the oxide-semiconductor film 14.

Then, as illustrated in FIG. 17, a gate insulating film 12 as a secondelectrical insulator is formed on the underlying insulating film 21 soas to cover the oxide-semiconductor film 14 therewith.

Then, a gate electrode 11 is formed on the gate insulating film 12.

Then, as illustrated in FIG. 18, an interlayer insulating film 23 isformed on the gate insulating film 12 so as to cover the gate electrode11 therewith.

Then, contact holes 19 are formed throughout the interlayer insulatingfilm 23 and the gate insulating film 12 such that the contact holes 19reach source/drain regions.

Then, as illustrated in FIG. 19, source and drain electrodes 16 areformed in the contact holes 19. Specifically, each of the source anddrain electrodes 16 is comprised of a metal plug formed in the contacthole 19 so as to reach the second interface layer 14E of theoxide-semiconductor film 14, and a layer formed on the interlayerinsulating film 23 and integrally with the metal plug.

Then, a protection insulating film 18 is formed on the interlayerinsulating film 23 so as to cover the source and drain electrodes 16therewith.

Thus, there is fabricated the thin-film device 300.

In the thin-film device 300 including a multi-layered structurecomprised of, in this order, the underlying insulating film (firstelectrical insulator) 21, the oxide-semiconductor film 14, the gateinsulating film (second electrical insulator) 12, the gate electrode 11,the interlayer insulating film 23, the source and drain electrodes 16,and the protection insulating film 18, it is possible to control thedefect (that is, generation of excessive electron donors) caused byoxygen holes existing at an interface between the oxide-semiconductorfilm 14 and the insulating films 21, 12.

Specifically, it is possible to reduce the defect caused by oxygen holesin the first interface layer 14A located at an interface with theunderlying insulating film 21, by carrying out the first oxidation 131illustrated in FIG. 15, and then, forming the oxide-semiconductor film14 as illustrated in FIG. 16. That is, a density of oxygen holes in thefirst interface layer 14A can be made smaller than a density of oxygenholes in the bulk layer 14B.

The second oxidation 132 illustrated in FIG. 16 makes it possible toreduce oxygen hole defect in the second interface layer 14E located atan interface with the gate insulating film 12 to thereby optimallyreduce an electron density in the second interface layer 14E, ensuringthat an off current of the thin-film device 300 caused by a back-channelelectron current can be effectively reduced.

Fourth Exemplary Embodiment

FIGS. 20 to 24 are cross-sectional views of a thin-film device 400, eachshowing a step to be carried out in a method of fabricating a thin-filmdevice 400 in accordance with the fourth exemplary embodiment.

A thin-film device 400 in the fourth exemplary embodiment is comprisedof a bottom gate planar type thin-film transistor.

Hereinbelow is explained a method of fabricating the thin-film device400.

First, as illustrated in FIG. 20, a gate metal film is formed on anelectrically insulating substrate 10, and then, the gate metal film ispatterned into a gate electrode 11.

Then, a gate insulating film 12 as a first electrical insulator isformed on the electrically insulating substrate 10 so as to cover thegate electrode 11 therewith.

Then, as illustrated in FIG. 21, a source/drain metal film is formed soas to entirely cover the gate insulating film 12 therewith, and then,the source/drain metal film is patterned into source/drain electrodes16, one of which is a source electrode and the other is a drainelectrode. The source and drain electrodes 16 are spaced away from eachother by an opening 16A.

Then, first oxidation 131 is applied to the gate insulating film 12.

The first oxidation 131 is comprised of application of oxygen plasma,for instance.

The first oxidation 131 causes oxygen to be adhered to a surface of thegate insulating film 12. This ensures that if oxygen deficiency weregenerated at a surface of the gate insulating film, 12, it would bepossible to remove the oxygen deficiency.

Following the first oxidation 131, as illustrated in FIG. 22, anoxide-semiconductor film 14 is formed on the gate insulating film 12without exposing to atmosphere.

Then, the oxide-semiconductor film 14 is patterned into such a shape asillustrated in FIG. 22.

As a result, a first interface layer 14A which is a portion of theoxide-semiconductor film 14 located at an interface with the gateinsulating film 12 is oxidized by oxygen having been adhered to asurface of the gate insulating film 12.

Thus, oxygen hole defect can be reduced in the first interface layer 14Aas a part of the oxide-semiconductor film 14.

Specifically, a density of oxygen holes in the first interface layer 14Aof the oxide-semiconductor film 14 becomes smaller than a density ofoxygen holes in a bulk layer 14B of the oxide-semiconductor film 14.

Then, as illustrated in FIG. 23, second oxidation 132 is applied to theoxide-semiconductor film 14. For instance, the second oxidation 132 iscomprised of application of oxygen plasma.

Then, as illustrated in FIG. 24, there is formed a protection insulatingfilm 18 as a second electrical insulator on the source and drainelectrodes 16 so as to cover the oxide-semiconductor film 14 therewithout exposing to atmosphere.

Thus, there is fabricated the thin-film device 400.

In the thin-film device 400 including a multi-layered structurecomprised of, in this order, the gate electrode 11, the gate insulatingfilm (first electrical insulator) 12, the source and drain electrodes16, the oxide-semiconductor film 14, and the protection insulating film(second electrical insulator) 18, it is possible to control the defect(that is, generation of excessive electron donors) caused by oxygenholes existing at an interface between the oxide-semiconductor film 14and the insulating films 12, 18.

Specifically, it is possible to reduce the defect caused by oxygen holesin the first interface layer 14A located at an interface with the gateinsulating film 12, by carrying out the first oxidation 131 illustratedin FIG. 21, and then, forming the oxide-semiconductor film 14 asillustrated in FIG. 22. That is, a density of oxygen holes in the firstinterface layer 14A can be made smaller than a density of oxygen holesin the bulk layer 14B.

The second oxidation 132 illustrated in FIG. 23 makes it possible toreduce oxygen hole defect in the second interface layer 14E located atan interface with the protection insulating film 18 to thereby optimallyreduce an electron density in the second interface layer 14E, ensuringthat an off current of the thin-film device 400 caused by a back-channelelectron current can be effectively reduced.

Fifth Exemplary Embodiment

In the above-mentioned first to fourth exemplary embodiments, theoxide-semiconductor film 14 in the thin-film devices 100, 200, 300 and400 is formed at a time, that is, formed as a single film. In the fifthembodiment described below, the oxide-semiconductor film 14 is formed ina plurality of steps, that is, formed as having a multi-layeredstructure.

Hereinbelow is explained a method of fabricating the oxide-semiconductorfilm 14 in the fifth embodiment.

First, as illustrated in FIG. 25, an extremely thin oxide-semiconductorfilm 51A is formed on a first electrical insulator 50.

The first electrical insulator 50 corresponds to the gate insulatingfilm 12 explained in the first embodiment (see FIG. 8) and the fourthembodiment (see FIG. 24), or to the underlying film 21 explained in thesecond embodiment (see FIG. 14) and the third embodiment (see FIG. 19).

Then, as illustrated in FIG. 26, oxidation 52 is applied to theoxide-semiconductor film 51A. For instance, the oxidation 52 iscomprised of application of oxygen plasma.

As a result, the oxide-semiconductor film 51A is oxidized at a surfacethereof.

Then, as illustrated in FIG. 27, an extremely thin oxide-semiconductorfilm 51B is formed on the oxide-semiconductor film 51A.

Then, the oxidation 52 is applied to the oxide-semiconductor film 51B,as illustrated in FIG. 28.

Then, as illustrated in FIG. 29, an extremely thin oxide-semiconductorfilm 51C is formed on the oxide-semiconductor film 51B.

The step of applying oxidation to a first thin oxide-semiconductor film,illustrated in FIG. 26, and the step of forming a second thinoxide-semiconductor film on the first thin oxide-semiconductor film,illustrated in FIG. 27, are repeatedly carried out by a requisite numberto thereby fabricate the oxide-semiconductor film 14.

In accordance with the fifth embodiment, since the oxide-semiconductorfilm 14 is formed by repeatedly alternately carrying out the formationof the oxide-semiconductor film and the application of the oxidation 52to the oxide-semiconductor film, it would be possible to sufficientlyoxidize each of the oxide-semiconductor films 51A, 51B and 51C, ensuringthe formation of the oxide-semiconductor film 14 having desiredfilm-characteristics.

In the above-mentioned first to fifth embodiments, theoxide-semiconductor film 14 may be composed of amorphous oxide orcrystalline oxide containing at least one of Zn, Ga and In.

The oxide-semiconductor film 14 may be fabricated, for instance, bysputtering, evaporation or chemical vapor deposition (CVD). Inparticular, the oxide-semiconductor film 14 composed of crystallineoxide can be fabricated by irradiating laser such as XeCl excimer laserto an amorphous film. This is because the oxide-semiconductor film 14 isalmost transparent to visible light, for instance, but is opaque to XeClexcimer laser having a wavelength of 308 nanometers, and hence, canabsorb the XeCl excimer laser.

It is also possible to crystallize the oxide-semiconductor film 14 byirradiating laser or light having a wavelength shorter than a wavelengthof visible lights to an amorphous film.

The oxide-semiconductor film 14 may be fabricated by dissolving powderedoxide-semiconductor into solvent, coating or printing the solventcontaining the oxide-semiconductor, onto a substrate, and heating thesolvent to thereby evaporate the solvent and allow only theoxide-semiconductor to remain on the substrate.

The oxidation in the above-mentioned first to fifth exemplaryembodiments may be comprised of application of oxidizing plasma, and thereduction in the above-mentioned first to fifth exemplary embodimentsmay be comprised of application of reducing plasma. The oxidizing plasmamay contain at least oxygen plasma or ozone plasma, for instance. Thereducing plasma may contain rare gas plasma such as Ar or He gas plasma,hydrogen gas plasma, and nitrogen gas plasma alone or in combination.

In the first to fifth exemplary embodiments, the first interface layer14A located at an interface with the first electrical insulator and thesecond interface layer 14E located at an interface with the secondelectrical insulator are smaller in a density of oxygen holes than thebulk layer 14B in the oxide-semiconductor film 14 sandwiched between thefirst electrical insulator (specifically, the gate insulating film 12 orthe underlying film 21) and the second electrical insulator(specifically, the protection insulating film 18 or the gate insulatingfilm 12). It should be noted that a density of oxygen holes in only oneof the first interface layer 14A and the second interface layer 14E maybe designed smaller than a density of oxygen holes in the bulk layer14B.

In the first to fifth exemplary embodiments, the gate insulating film 12or the underlying insulating film 21 as the first electrical insulatoris formed on the electrically insulating substrate 10. As analternative, the electrically insulating substrate 10 may be comprisedof the first electrical insulator. However, from the viewpoint of afabrication yield and stability of characteristics, it is preferable toform the first electrical insulator (for instance, the gate insulatingfilm 12 or the underlying film 21) on the electrically insulatingsubstrate 10.

In the above-mentioned first to fifth exemplary embodiments, thethin-film devices 100, 200, 300 and 400 are comprised of a thin-filmtransistor. As an alternative, the thin-film devices 100, 200, 300 and400 may be comprised of a thin-film diode.

In the specification, the term “oxide” includes “dioxide”.

Example 1

Example 1 is explained hereinbelow with reference to FIGS. 1 to 8.

First, as illustrated in FIG. 1, a Cr metal film as a gate metal filmwas formed by sputtering on a glass substrate as an electricallyinsulating substrate 10, and then, the Cr metal film was patterned by aphotolithography step into a gate electrode 11.

Then, a silicon nitride film a gate insulating film 12 was formed bysputtering on the electrically insulating substrate 10 so as to coverthe gate electrode 11 therewith. The silicon nitride film had athickness of 300 nanometers.

Then, as illustrated in FIG. 2, first oxidation 131 was applied to thegate insulating film 12 without exposing to atmosphere to therebyoxidize the silicon nitride film at a surface thereof. The firstoxidation 131 was comprised of application of oxygen plasma.

Following the first oxidation 131, as illustrated in FIG. 3, anoxide-semiconductor film 14 was formed by sputtering on the gateinsulating film 12 without exposing to atmosphere. Theoxide-semiconductor film 14 was composed of InGaZnO₄, and had athickness of 100 nanometers.

Sintered InGaZnO₄ was used as a target in sputtering. Theoxide-semiconductor film 14 may be fabricated by carrying out sputteringseparately through the use of oxides of In, Ga and Zn as a target tothereby react them with one another on the electrically insulatingsubstrate 10.

The step of forming the silicon nitride film, the application of oxygenplasma to the gate insulating film 12, and the step of forming theoxide-semiconductor film 14 composed of InGaZnO₄ can be successivelycarried out without exposing to atmosphere by carrying out them in acommon sputtering apparatus kept in vacuum (that is, kept in a reducepressure), for instance.

Then, as illustrated in FIG. 4, the oxide-semiconductor film 14 waspatterned by a photolithography step into a desired island.

Then, as illustrated in FIG. 5, reduction 15 was applied to theoxide-semiconductor film 14. The reduction 15 was comprised ofapplication of Ar plasma.

The application of Ar plasma to the oxide-semiconductor film 14generated oxygen holes at a surface 14C of the oxide-semiconductor film14 with the result that a resistivity at the surface 14C of theoxide-semiconductor film 14 was reduced to about 1/1000. Thus,source/drain regions could have an optimal resistivity.

Following the application of Ar plasma to the oxide-semiconductor film14, a Cr film as a source/drain metal film was formed so as to entirelycover the gate insulating film 12 and the oxide-semiconductor film 14therewith out exposing to atmosphere, and then, the Cr film waspatterned into source/drain electrodes 16, as illustrated in FIG. 6.

Then, as illustrated in FIG. 7, second oxidation 132 was applied to thesurface 14C of the oxide-semiconductor film 14 through an opening 16Aformed between the source and drain electrodes 16. The second oxidation132 was comprised of application of oxygen plasma.

The second oxidation 132 was carried out for the purpose of oxidizingthe surface 14C (namely, a second interface layer 14E) of theoxide-semiconductor film 14 through the opening 16A to thereby reduceexcessive donor electrons caused by oxygen holes. By reducing oxygenholes, it was possible to reduce an off current of the thin-film device100 by about two columns.

Then, as illustrated in FIG. 8, there was subsequently formed aprotection insulating film 18 by sputtering without exposing toatmosphere so as to cover the source and drain electrodes 16 and theoxide-semiconductor film 14 therewith. The protection insulating film 18was comprised of a silicon nitride film, and had a thickness of 300nanometers.

Thus, there was fabricated the thin-film transistor 100.

Example 2

Example 2 is explained hereinbelow with reference to FIGS. 9 to 14.

As illustrated in FIG. 9, an underlying insulating film 21 comprised ofa silicon nitride film was formed by sputtering on a resin substrate asan electrically insulating substrate 10 by a thickness of 300nanometers. Then, a Mo metal film was formed on the underlyinginsulating film 21, and subsequently, the Mo metal film was patternedinto source and drain electrodes 16 by a photolithography step.

Then, as illustrated in FIG. 10, first oxidation 131 was applied to theunderlying insulating film 21 through an opening 16A formed between thesource and drain electrodes 16.

The first oxidation 131 was comprised of application of oxygen plasma.

Following the first oxidation 131, an oxide-semiconductor film 14composed of InGaZnO₄ was formed by sputtering at room temperature on theunderlying insulating film 21 and the source/drain electrodes 16 withoutexposing to atmosphere. The oxide-semiconductor film 14 had a thicknessof 60 nanometers. Then, the oxide-semiconductor film 14 was patternedinto a desired island, as illustrated in FIG. 11.

Then, as illustrated in FIG. 12, second oxidation 132 was applied to asurface (second interface layer 14E) of the oxide-semiconductor film 14.The second oxidation 132 was comprised of application of oxygen plasma.As a result, the surface of the oxide-semiconductor film 14 was oxidizedwith the result of reduction in oxygen holes existing at the surface ofthe oxide-semiconductor film 14.

Then, as illustrated in FIG. 13, there was formed a gate insulating film12 by sputtering without exposing to atmosphere so as to cover theoxide-semiconductor film 14 and the source and drain electrodes 16therewith. The gate insulating film 12 was comprised of a siliconnitride film, and had a thickness of 400 nanometers.

Then, as illustrated in FIG. 14, a gate electrode 11 composed ofaluminum was formed on the gate insulating film 12.

Then, a protection insulating film 18 was formed by sputtering on thegate insulating film 12 so as to cover the gate electrode 11 therewith.The protection insulating film 18 was comprised of a silicon nitridefilm, and had a thickness of 300 nanometers.

Thus, there was fabricated the thin-film device 200.

By carrying out the first and second oxidation 131 and 132, it waspossible to control a density of electrons in a channel region of thethin-film device 100, ensuring switching characteristics in which anON/OFF ratio of a drain current had five or more columns.

In order to enhance the switching characteristics, theoxide-semiconductor film 14 is formed by a thickness of 60 nanometers,and immediately thereafter, oxygen plasma is applied to theoxide-semiconductor film 14. Then, the gate insulating film 12 composedof silicon nitride is partially formed as a first gate insulating film.The gate insulating film 12 has a thickness of 50 nanometers.

Then, a multi-layered structure including the oxide-semiconductor film14, and the gate insulating film 12 formed on the oxide-semiconductorfilm 14 is patterned into a desired island. Then, the rest of the gateinsulating film 12 composed of silicon nitride is formed by a thicknessof 350 nanometers as a second gate insulating film.

The thus formed gate insulating film in the thin-film device 200 has atotal thickness of 400 nanometers. The thus formed gate insulating filmis identical in thickness to the gate insulating film 12 in Example 2,but is different from the gate insulating film 12 in Example 2 in thatan interface between the oxide-semiconductor film 14 and the gateinsulating film 12 is never exposed to atmosphere. In Example 2, anupper surface of the oxide-semiconductor film 14 is exposed toatmosphere or a photolithography process when the oxide-semiconductorfilm 14 is patterned.

By preventing an interface between the oxide-semiconductor film 14 andan insulating film (for instance, the gate insulating film 12) frombeing exposed to atmosphere, it would be possible to suppress generationof oxygen hole defect and other impurity defects, ensuring qualifiedswitching characteristics.

Example 3

Example 3 is explained hereinbelow with reference to FIGS. 15 to 19.

First, as illustrated in FIG. 15, an underlying insulating film 21 wasformed by sputtering on a glass substrate as an electrically insulatingsubstrate 10. The underlying insulating film 21 was comprised of asilicon nitride film, and had a thickness of 300 nanometers.

Then, first oxidation 131 was applied to a surface of the underlyinginsulating film 21 to thereby oxidize a surface of the underlyinginsulating film 21. The first oxidation 131 was comprised of applicationof oxygen plasma.

Then, as illustrated in FIG. 16, an oxide-semiconductor film 14 composedof InGaZnO₄ was formed by sputtering at room temperature on theunderlying insulating film 21 by a thickness of 60 nanometers.

The amorphous oxide-semiconductor film 14 was crystallized byirradiating XeCl excimer laser to the oxide-semiconductor film 14, andfusing and solidifying the same.

Then, as illustrated in FIG. 16, the polycrystal oxide-semiconductorfilm 14 was patterned into a desired island.

Then, as illustrated in FIG. 16, second oxidation 132 was applied to thepolycrystal oxide-semiconductor film 14 to thereby oxidize a surface ofthe polycrystal oxide-semiconductor film 14 for reducing oxygen holedefect. The second oxidation 132 was comprised of application of oxygenplasma.

The application of oxygen plasma is quite effective when theoxide-semiconductor film 14 composed of InGaZnO₄ is crystallized byirradiating laser thereto, since oxygen escapes in a high-temperaturemolten state.

Following the second oxidation 132, as illustrated in FIG. 17, a gateinsulating film 12 comprised of a silicon nitride film was formed bysputtering on the underlying insulating film 21 by a thickness of 100nanometers without exposing to atmosphere so as to cover theoxide-semiconductor film 14 therewith.

Then, a gate electrode 11 composed of aluminum was formed on the gateinsulating film 12.

Then, as illustrated in FIG. 18, an interlayer insulating film 23comprised of a silicon oxide film was formed on the gate insulating film12 by a thickness of 400 nanometers so as to cover the gate electrode 11therewith.

Then, contact holes 19 were formed throughout the interlayer insulatingfilm 23 and the gate insulating film 12 such that the contact holes 19reach source/drain regions.

Then, as illustrated in FIG. 19, source and drain electrodes 16 wereformed in the contact holes 19. Specifically, each of the source anddrain electrodes 16 was comprised of a metal plug formed in the contacthole 19 so as to reach the second interface layer 14E of theoxide-semiconductor film 14, and a layer formed on the interlayerinsulating film 23 and integrally with the metal plug.

Then, a protection insulating film 18 comprised of a silicon nitridefilm was formed on the interlayer insulating film 23 so as to cover thesource and drain electrodes 16 therewith. The protection insulating film18 had a thickness of 300 nanometers.

Thus, there was fabricated the thin-film device 300.

Since the oxide-semiconductor film 14 was crystallized in Example 3,electron mobility obtained in Example 3 was about five to ten timesgreater than electron mobility obtained in Examples 1 and 2.

The thin-film device in accordance with the above-mentioned first tofifth embodiments and Examples 1 to 3 may be applicable to a pixeldriver to be used in a flat panel display such as a liquid crystaldisplay or an organic electroluminescence (EL) display. In particular,since oxide-semiconductor is transparent, a pixel driver of a liquidcrystal display to which the thin-film device is applied ensures higherback-light transmissivity than a pixel driver to which conventionalsilicon semiconductor is applied, presenting a brighter high-performancedisplay. Such a driver may be comprised of a thin-film diode includingtwo terminals, as well as a thin-film transistor including threeterminals.

An oxide-semiconductor film, even when it was formed at roomtemperature, has electron mobility greater by about one column than thesame of conventionally used amorphous silicon formed at 300 degreescentigrade. Hence, it is possible to fabricate a thin-film transistorarray having superior characteristics, even if it was fabricated at roomtemperature. In particular, it would be possible to control a density ofoxygen holes by a low-temperature process in an interface ofoxide-semiconductor on which electrical characteristics of a thin-filmtransistor is dependent. Accordingly, desired characteristics can beobtained in a thin-film device including a resin substrate having lowresistance to heat, and hence, the thin-film device in accordance withthe above-mentioned embodiments can be applied to a display including aflexible resin substrate.

In the thin-film device in accordance with the above-mentioned exemplaryembodiment, it is preferable that oxygen hole densities in both of thefirst and second interlayer layers are smaller than a density of oxygenholes in the bulk layer.

For instance, the oxide-semiconductor film may be composed of amorphousoxide containing at least one of Zn, Ga and In.

As an alternative, the oxide-semiconductor film may be composed ofcrystalline oxide containing at least one of Zn, Ga and In.

In the thin-film device in accordance with the above-mentioned exemplaryembodiment, it is preferable that the oxide-semiconductor film is formedby crystallizing amorphous oxide with laser irradiation thereto.

In the thin-film device in accordance with the above-mentioned exemplaryembodiment, it is preferable that the oxide-semiconductor film is formedby dissolving powdered oxide semiconductor into solvent, coating orprinting the solvent onto the first electrical insulator, and heatingthe solvent to vaporize the solvent.

In the thin-film device in accordance with the above-mentioned exemplaryembodiment, it is preferable that the first electrical insulator, theoxide-semiconductor film, and the second electrical insulator are formedon an electrically insulating substrate.

In the thin-film device in accordance with the above-mentioned exemplaryembodiment, it is preferable that the electrically insulating substrateis comprised of one of a glass substrate and a resin substrate.

In the thin-film device in accordance with the above-mentioned exemplaryembodiment, it is preferable that the thin-film device is comprised ofone of a thin-film transistor and a thin-film diode.

In the method of fabricating a thin-film device, in accordance with theabove-mentioned exemplary embodiment, it is preferable that theoxidizing is comprised of a step of applying plasma to theoxide-semiconductor film in which one of oxygen plasma and ozone plasmais used.

In the method of fabricating a thin-film device, in accordance with theabove-mentioned exemplary embodiment, it is preferable that the firstelectrical insulator, the oxide-semiconductor film, and the secondelectrical insulator are formed by forming, in sequence, a gate metalfilm, a gate insulating film as the first electrical insulator, theoxide-semiconductor film, a source/drain metal film, and a protectioninsulating film as the second electrical insulator, and wherein theoxidizing and the formation of the oxide-semiconductor film are carriedout in this order without exposing the oxide-semiconductor film toatmosphere after the formation of the gate insulating film.

In the method of fabricating a thin-film device, in accordance with theabove-mentioned exemplary embodiment, it is preferable that the firstelectrical insulator, the oxide-semiconductor film, and the secondelectrical insulator are formed by forming, in sequence, a gate metalfilm, a gate insulating film as the first electrical insulator, theoxide-semiconductor film, a source/drain metal film, and a protectioninsulating film as the second electrical insulator, and whereinreduction to the oxide-semiconductor film and the formation of thesource/drain metal film are carried out in this order without exposingthe oxide-semiconductor film and the source/drain metal film toatmosphere after the oxide-semiconductor film was patterned.

In the method of fabricating a thin-film device, in accordance with theabove-mentioned exemplary embodiment, it is preferable that thereduction to the oxide-semiconductor film is comprised of a step ofapplying plasma to the oxide-semiconductor film in which at least one ofrare gas plasma, hydrogen gas plasma, and nitrogen gas plasma alone orin combination is used.

In the method of fabricating a thin-film device, in accordance with theabove-mentioned exemplary embodiment, it is preferable that the firstelectrical insulator, the oxide-semiconductor film, and the secondelectrical insulator are formed by forming, in sequence, a gate metalfilm, a gate insulating film as the first electrical insulator, theoxide-semiconductor film, a source/drain metal film, and a protectioninsulating film as the second electrical insulator, and wherein theoxidizing and the formation of the protection insulating film arecarried out in this order without exposing the oxide-semiconductor filmand the protection insulating film to atmosphere after the source/drainmetal film was patterned.

In the method of fabricating a thin-film device, in accordance with theabove-mentioned exemplary embodiment, it is preferable that the firstelectrical insulator, the oxide-semiconductor film, and the secondelectrical insulator are formed by forming, in sequence, an underlyingelectrically insulating film as the first electrical insulator, asource/drain metal film, the oxide-semiconductor film, a gate insulatingfilm as the second electrical insulator, a gate metal film, and aprotection insulating film, and wherein the oxidizing and the formationof the gate insulating film are carried out in this order withoutexposing the oxide-semiconductor film and the gate insulating film toatmosphere after the formation of the oxide-semiconductor film.

In the method of fabricating a thin-film device, in accordance with theabove-mentioned exemplary embodiment, it is preferable that the firstelectrical insulator, the oxide-semiconductor film, and the secondelectrical insulator are formed by forming, in sequence, an underlyingelectrically insulating film as the first electrical insulator, asource/drain metal film, the oxide-semiconductor film, a gate insulatingfilm as the second electrical insulator, a gate metal film, and aprotection insulating film, and wherein the oxidizing and the formationof the oxide-semiconductor film are carried out in this order withoutexposing the oxide-semiconductor film to atmosphere after thesource/drain metal film was patterned.

In the method of fabricating a thin-film device, in accordance with theabove-mentioned exemplary embodiment, it is preferable that the firstelectrical insulator, the oxide-semiconductor film, and the secondelectrical insulator are formed by forming, in sequence, an underlyingelectrically insulating film as the first electrical insulator, theoxide-semiconductor film, a gate insulating film as the secondelectrical insulator, a gate metal film, an interlayer insulating film,a source/drain metal film, and a protection insulating film, and whereinthe oxidizing and the formation of the oxide-semiconductor film arecarried out in this order without exposing the oxide-semiconductor filmto atmosphere after the formation of the underlying electricallyinsulating film.

In the method of fabricating a thin-film device, in accordance with theabove-mentioned exemplary embodiment, it is preferable that the firstelectrical insulator, the oxide-semiconductor film, and the secondelectrical insulator are formed by forming, in sequence, an underlyingelectrically insulating film as the first electrical insulator, theoxide-semiconductor film, a gate insulating film as the secondelectrical insulator, a gate metal film, an interlayer insulating film,a source/drain metal film, and a protection insulating film, and whereinthe oxidizing and the formation of the gate insulating film are carriedout in this order without exposing the oxide-semiconductor film and thegate insulating film to atmosphere after the formation of theoxide-semiconductor film.

In the method of fabricating a thin-film device, in accordance with theabove-mentioned exemplary embodiment, it is preferable that the firstelectrical insulator, the oxide-semiconductor film, and the secondelectrical insulator are formed by forming, in sequence, a gate metalfilm, a gate insulating film as the first electrical insulator, asource/drain metal film, the oxide-semiconductor film, and a protectioninsulating film as the second electrical insulator, and wherein theoxidizing and the formation of the oxide-semiconductor film are carriedout in this order without exposing the oxide-semiconductor film toatmosphere after the source/drain metal film was patterned.

In the method of fabricating a thin-film device, in accordance with theabove-mentioned exemplary embodiment, it is preferable that the firstelectrical insulator, the oxide-semiconductor film, and the secondelectrical insulator are formed by forming, in sequence, a gate metalfilm, a gate insulating film as the first electrical insulator, asource/drain metal film, the oxide-semiconductor film, and a protectioninsulating film as the second electrical insulator, and wherein theoxidizing and the formation of the protection insulating film arecarried out in this order without exposing the oxide-semiconductor filmand the protection insulating film to atmosphere after theoxide-semiconductor film was patterned.

The exemplary advantages obtained by the above-mentioned exemplaryembodiments are described hereinbelow.

The thin-film device and the method of fabricating the same both inaccordance with the above-mentioned exemplary embodiments make itpossible to control the defect (that is, generation of excessiveelectron donors) caused by oxygen holes existing at an interface betweenan oxide-semiconductor film and an electrically insulating film.Specifically, it is possible to suppress generation of oxygen holes in aregion in which generation of oxygen holes is not required. Thus, it ispossible to fabricate a thin-film device having desired characteristics,with high reproducibility and high fabrication yield.

While the present invention has been described in connection withcertain exemplary embodiments, it is to be understood that the subjectmatter encompassed by way of the present invention is not to be limitedto those specific embodiments. On the contrary, it is intended for thesubject matter of the invention to include all alternatives,modifications and equivalents as can be included within the spirit andscope of the following claims.

This application is based upon and claims the benefit of priority fromJapanese Patent Application No. 2006-217272 filed on Aug. 9, 2006, theentire disclosure of which, including specification, claims, drawingsand summary, is incorporated herein by reference in its entirety.

What is claimed is:
 1. A method of fabricating a thin-film device,including: forming an oxide-semiconductor film on a first electricalinsulator; forming a second electrical insulator on saidoxide-semiconductor film, said oxide-semiconductor film defining anactive layer, said oxide-semiconductor film being comprised of a firstinterface layer located at an interface with said first electricalinsulating insulator, a second interface layer located at an interfacewith said second electrical insulator, and a bulk layer other than saidfirst and second interface layers; and oxidizing saidoxide-semiconductor film to render a density of oxygen holes in at leastone of said first and second interlayer layers smaller than a density ofoxygen holes in said bulk layer, wherein said first electricalinsulator, said oxide-semiconductor film, and said second electricalinsulator are formed by forming, in sequence, a gate metal film, a gateinsulating film as said first electrical insulator, saidoxide-semiconductor film, a source/drain metal film, and a protectioninsulating film as said second electrical insulator, and wherein saidoxidizing and the formation of said protection insulating film arecarried out in this order without exposing said oxide-semiconductor filmand said protection insulating film to atmosphere after saidsource/drain metal film was patterned.